1. Field of the Invention
This invention relates to interlock systems, and it relates especially, though not exclusively, to such systems as are intended for use as safety measures in domestic electrical appliances, such as food processors, food mixers, blenders and the like; in general any appliance that has moving parts and/or heating elements that could, under certain operational circumstances, cause harm to a user in the absence of the interlock system. The invention also encompasses a domestic electrical appliance incorporating such an interlock system.
2. Description of the Related Art
Interlock systems are an essential feature of many domestic appliances, and their components need to satisfy demanding, and sometimes opposing, operational, regulatory, economic and aesthetic criteria. Hence difficulties arise in providing interlock systems that are sufficiently robust and reliable to meet user demands and comply with stringent regulatory stipulations, whilst being economical to produce and conforming to an acceptable aesthetic design.
Many interlock systems have been devised hitherto for sensing when safe and unsafe conditions obtain in domestic electrical food preparation equipment and the like. A typical condition required to be sensed with such equipment is the presence or absence of a lid or cover on a receptacle within which a processing tool is to be rotated or otherwise moved by means of an electric motor. Typically, such tools are driven at relatively high speeds and contain sharply edged blades or rasp-like features which are intended to cut, mash or otherwise comminute food items placed in the receptacle for processing. Accordingly, dangerous situations can arise if such tools are operated whilst the receptacle is open, and thus it is standard practice to provide the lid or cover with some kind of actuator which operates, directly or indirectly, on an interlock switch means, such that the supply of electrical current to the motor is interrupted unless the lid or cover is securely in place upon the receptacle.
It will be appreciated that, where the aforementioned actuator associated with the lid or cover operates directly upon the interlock switch means, it is necessary either to dispose the switch means near the lid or cover or to have the actuator carry a significant extension piece that can reach a more remotely-located switch means. For various reasons, neither configuration is particularly attractive for practical use, and thus the majority of equipment utilizes indirect operation.
Indirect operation implies that the actuator associated with the lid or cover operates an intermediate member which then, in turn, operates the switch means. Again, many different types of intermediate member have been tried, such as levers, push-rods and the like; though difficulties remain in providing a system which can accurately and reliably convey the status of the actuator to the switch means by way of a mechanism which is rugged, reliable, cost-effective, resistive to (or insensitive to) the ingress of food or other products processed by the equipment, aesthetically acceptable and which cannot readily be compromised (accidentally or deliberately) by users.
Typically, the lid or cover for the receptacle is formed with an upstanding, chimney-like feed-tube through which food items can be added for processing in the receptacle. A “pusher”, typically of plastics material and sized to fit closely within the feed tube, is further provided, by means of which a user can urge foodstuffs down into the receptacle for processing. Such feed tubes provide direct access to the interior of the receptacle and thus, in principle, can compromise operational safety. Many such tubes, however, are dimensionally conFig.d to be relatively narrow in breadth and relatively tall in height, so that any such compromise is minimal.
There is, however, a demand for food preparation equipment provided with a wide feed-tube and associated pusher, to enable relatively bulky food items to be added to the receptacle for processing. Such equipment presents special difficulties as regards the interlock requirements, since there is now a need to detect not only that the lid or cover is in place, but also that a pusher has been inserted into the feed tube, before the motor can be driven. Thus, a dual interlock system is required.
U.S. Pat. No. 4,216,917 describes a dual interlock system, in which a wide feed tube is made safe by virtue of an interlock which recognizes the presence of a pusher in the feed tube. The prior art system provides a vertical rib on the side of the pusher, which enters a corresponding vertical channel extending down the side of the feed-tube and actuates a spring-loaded operator member, extending it downwards. This in turn acts on a cam member which bears down on a main interlock rod, extending down the side of the receptacle, which actuates a cut-out switch.
The prior art system is quite complex and it is desirable, from the standpoints of both economy and reliability, to provide an improved system.